Preparation of beryllium bis(dihydrocarbyl borohydride)

ABSTRACT

1. PROCESS FOR THE PREPARATION OF BERYLLIUM BIS(DIHYDROCARBYL BOROHYDRIDE) OF THE GENERAL FORMULA   BE(BR2H2)2.   WHEREIN R REPRESENTS A RADICAL SELECTED FROM THE GROUP CONSISTING OF ALKYL, MONOCYCLIC CYCLOALKYL AND MONOCYCLIC ARYL RADICALS CONTAINING FROM 1 TO ABOUT 10, 5 TO ABOUT 10 AND 6 TO ABOUT 10 CARBON ATOMS, RESPECTIVELY, WHICH COMPRISES ADDING A DIHYDROCARBYL BERYLLIUM COMPOUND OF THE GENERAL FORMULA R2BE TO A MINOR EXCESS OF A TETRAORGANODIBORANE OF THE GENERAL FORMULA R4B2H2, SAID ADDITION BEING CARRIED OUT AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 0 TO ABOUT 110*C., MAINTAINING THE REACTION MIXTURE AT SAID TEMPERATURE FOR A PERIOD RANGING FROM LESS THAN 0.25 TO MORE THAN 24 HOURS SUFFICIENT TO ASSURE THE SUBSTANTIAL COMPLETION OF THE REACTION AND RECOVERING THE BERYLLIUM BIS(DIHYDROCARBYL BOROHYDRIDE) FROM THE REACTION MIXTURE.

United States Patent Oflice 3,847,998 PREPARATION OF BERYLLIUMBIS(DIHYDRO- CARBYL BOROHYDRIDE) Lawrence H. Shepherd, Jr., and PaulKobetz, Baton Rouge, and Roy J. Laran, Greenwell Springs, La., andRobert W. Johnson, Jr., Savannah, Ga., assignors to Ethyl Corporation,New York, N.Y.

No Drawing. Original application Jan. 27, 1965, Ser. No. 430,237.Divided and this application Nov. 18, 1965,

Ser. No. 537,576

Int. Cl. C07d 105/02 US. Cl. 260-6065 B 2 Claims This application is adivision of our application Ser. N0. 430,237, filed Ian. 27, 1965.

This invention relates to and has as its principal objects the provisionof a novel composition of matter, beryllium bis(diethylborohydride), andof a method of preparing the same, and the provision of a novel andeffective process for the production of beryllium hydride of highpurity.

In accordance with the present invention, a berylliumbis(diorganoborohydride) is produced by the reaction, at a temperaturebetween ambient temperature and the decomposition temperature of theproduct, of a tetraorganodiborane of the general formula R B H with adiorganoberyllium compound of the general formula R Be wherein R and Rare alkyl, monocyclic cycloalkyl, or monocyclic aryl radicals,containing from 1 to about 10, 5 to about or 6 to about 10 carbon atoms,respectively. After reaction is complete, the berylliumbis(diorganoborohydride) product is recovered from the reaction mixtureby removal of the triorganoborane by-product under vacuum or by othersuitable separatory procedure.

If the product of the foregoing reaction is subjected to thermaldecomposition, or if the above process is carried out ab initio at atemperature above the thermal decomposition temperature of said product,beryllium hydride of high purity is obtained.

It has been found, for example, that when tetraethyl diborane, Et B Hdissolved in toluene, is treated with a toluene solution of diethylberyllium, the mixture is heated to about 110 C. so as to complete thereaction and the reaction mixture is subjected to vacuum distillation,beryllium hydride of a purity in excess of 80 percent by weight isobtained. Since beryllium hydride is very useful in the chemical andallied arts, the improved preparative process of the present inventionconstitutes a valuable addition to the art.

The reaction of the instant invention has a number of important andadvantageous features. Among these are the ease of preparation andpurification of the reactants and the possibility of recycling theorganoborane byproducts, thus avoiding Waste of an intrinsicallyexpensive material and thereby increasing significantly the economy ofthe overall process.

The invention will be more fully understood by reference to thefollowing illustrative examples in which all parts and percentages areby weight.

EXAMPLE I Preparation of Tetraethyl Diborane' Tetraethyldiborane wasprepared as described by Koster et al., Ann. 644, (1961).

3,847,998 Patented Nov. 12, 1974 Triethylborane was hydrogenated under5000 p.s.i.g. at to 185 C. to a mixture of triethyldiborane andtetraethyldiborane. Sufficient triethylborane was then added to themixture of organodiboranes to convert the triethyl diborane present totetraethyl diborane.

The product was a colorless pyropho'ric liquid with a boiling point of111 C. Analysis of the tetraethyl diborane was accomplished by measuringthe amount of gas liberated upon hydrolysis of a weighed sample. Thepurity was found to be 99 weight percent, the remainder of the samplebeing triethylborane.

EXAMPLE II Preparation of Beryllium Hydride Into a suitable reactor wereintroduced 7.19 parts (51.3 rnillimoles) of tetraethyl diboranedissolved in 130 parts of dry toluene. The solution was stirred at roomtemperature while 3.09 parts (46.0 rnillimoles) of diethyl berylliumwere added dropwise. After the addition was complete, the solution washeated to boiling with continued stirring for a period of thirtyminutes. Approximately two-thirds of the toluene was removed bydistillation. The precipitated beryllium hydride was separated byfiltration, washed several times on the filter with dry pentane, anddried overnight under vacuum at room temperature. After further dryingfor three hours at to 185 C., under a pressure of 0.1 mm. of mercury,the product analyzed, by hydrolysis, 82.7 Weight percent of berylliumhydride and 1.3 percent of diethyl beryllium.

When the experiment of Example II is repeated, replacing the ethylgroups of the two reactants with isobutyl, cyclohexyl, or phenylradicals, similar results are obtained.

When the experiment of Example II is repeated with reversal of the orderof addition, so that the tetraethyl diborane is added to the diethylberyllium, beryllium hydride precipitates immediately, but the productis less pure than that obtained by the procedure of Example II, which istherefore preferred.

EXAMPLE III Preparation of Beryllium Hydride Example II was repeatedusing equimolar amounts of tetraethyldi-borane (6.99 parts) and diethylberyllium (3.36 parts) the former being dissolved in 43.4 parts oftoluene. The beryllium hydride so produced, after vacuum treatment at150 for two hours and then at for two hours under a pressure of 0.1 mm.of mercury, analyzed 79.4 percent pure.

When Example III was repeated reversing the order of addition of thereactants, namely, adding the tetraethyl diborane to the diethylberyllium, the purity of the resultant beryllium hydride was reduced to32.2 percent.

When Example H was repeated using only a 1.8 percent excess oftetraethyldiborane, the purity of the beryllium hydride product was 76.5percent.

EXAMPLE IV Tetraethyldiborane (28.8 parts, 206 rnillimoles) wasintroduced into a suitable reactor equipped With a stirrer and a refluxcondenser. 6.91 parts (103 rnillimoles) of diethylberyllium were addeddropwise with continuous agitation and external cooling by means of anice bath. When reaction was complete, the volatile products wereseparated by evacuation at room temperature, and were condensed in aDry-Ice trap. Analysis of the residue in the trap by acidhydrolysisshowed 2 percent of tetra ethyl diborane; the remainder wastriethylborane.

The residue in the reactor was a colorless liquid which was identified,by hydrolysis and molecular weight determination, as berylliumbis(diethyl borohydride),

Be(Bet H 2- Hydrolysis of the product yielded 26.0 millimoles ofhydrogen per gram. Theory for Be(BEt H is 26.5 millimoles per gram.

The molecular weight of the product was found, by cryoscopicdetermination in benzene, to be 151.5225. Theory for Be-(BEt I-l is 151.

When the experiment of Example IV is repeated, replacing thetetraethyldiborane with and replacing the diethylberyllium withdimethylberyllium, diisobutylberyllium, dineopentylberyllium,bis(2-ethylhexyl) beryllium, di-n-decylberyllium,dicyclopentylberyllium, dicyclopentadienylberyllium,dicyclohexylberyllium, bis(methylcyclopentyl) beryllium, bis(dimethylcyclohexyl) beryllium, bis(isobutylcyclohexyl) beryllium,diphenylberyllium, di-o-tolyl-beryllium, -bis(2,4-xylyl) beryllium,dimesitylberyllium, or diisodurylberyllium,

similar results are obtained.

EXAMPLE V The beryllium bis(diethylborohydride) (1.51 parts, 100millimoles) obtained by the procedure of Example IV was placed under areduced pressure of 40 to 60 millimeters or mercury and heatedgradually, over a period of four to six hours, to 180 C. The product wasberyllium hydride of a purity in excess of 71 percent by Weight.

When the experiment of Example V is repeated, replacing the ethyl groupsof the beryllium bis(diethylborohydride) with isobutyl, cyclohexyl orphenyl radicals, similar results are obtained.

The reactants employed in the process of this invention comprise, asindicated above, a tetraorganodiborane of the general formula R B H anda diorganoberyllium compound of the general formula R 'Be. The organicmoieties, R and R, of these reactants may be any of a wide variety oforganic radicals. Thus the tetraorganodiboranes are exemplified bytetramethyldiborane, tetra-n-propyldiborane, tetraisobutyldiborane,

tetra-n-octyl diborane, tetraisononyldiborane,

tetra-n-decyl diborane, tetracyclopentyldiborane,tetracyclohexyldiborane, tetra(methylcyclohexyl) diborane,tetra(ethylcyclohexyl) diborane, tetra(isopropyl cyclohexyl) diborane,tetra(isopropyl cyclopentyl) diborane, tetra(n-butyl cyclohexyl)diborane, tetra(diethyl cyclohexyl) diborane, tetraphenyldiborane,

tetraorthotolyl diborane,

tetra (2,4-xylyl) diborane, tetra-p-cumenyl diborane,tetramesityldiborane and tetraduryldiborane.

Similarly the diorganoberyllium reactants are exemplified bydimethylberyllium,

di-n-propyl beryllium, diisobutylberyllium,

di-tert-butyl beryllium, diisoamylberyllium,

di-n-octyl beryllium,

di-isodecyl beryllium, methylethylberyllium, methylisohexyl beryllium,isopropylheptyl beryllium, dicyclopentyl beryllium,

cyclopentyl methylcyclopentyl beryllium, bis(methylcyclopentyl)beryllium, bis(cyclohexyl) beryllium, bis(ethylcyclohexyl) beryllium,bis(isopropyl cyclohexyl) beryllium, bis(n-butyl cyclohexyl) beryllium,diphenylberyllium,

diorthotolyl beryllium,

di-p-tolyl beryllium,

di-2,3-xylyl beryllium, bis(ortho-n-butyl phenyl) beryllium and his(diethylphenyl) beryllium.

In carrying out the process of this invention, the ratio of thereactants can be varied Within wide limits, namely, from the amountstoichiometrically required to a 100 percent or greater excess thereoverof the tetraorganodiborane reactant. The use of stoichiometricquantities yields satisfactory results, but a moderate excess, of theorder of about 10 percent of the tetraorganodiborane reactant increasesthe rate and degree of completeness of the reaction and is thereforepreferred.

A Wide variety of temperatures can be employed in the process of theinvention. The applicable range depends upon the particular reactantsand pressure employed and upon whether or not it is desired to isolatethe borohydride intermediate.

When the product sought is beryllium hydride, the reaction temperaturecan range from about 75 to about 200 C. and the pressure from about 0.1mm. of mercury to about 10 atmospheres. When the reactants are diethylberyllium and tetraethyl diborane, the preferred range is from about 75to about C. and the preferred pres sure about atmospheric. Higher alkylderivatives require, in general, higher upper temperature limits forcompleteness of reaction. Atmospheric pressure is generauy preferredbecause of the ease of operation associated therewith.

When the borohydride product is desired, the temperature must,evidently, not exceed the decomposition temperature thereof, and thislargely depends on the identities of the reactants and of the particularberyllium bis(di hydrocarbyl borohydride) to be prepared. In the case ofthe diethyl derivative, the temperature can range from about 0 to about75 C. and the pressure from mm. of mercury or below to 5 atmospheres orabove. Atmospheric pressure and temperatures in the range of from aboutto about 75 C. are preferred because such conditions provide bothstability of the product and a practical reaction rate.

The reaction time for the preparation of either the boro hydride orberyllium hydride can range from 15 minutes or less to 24 hours or more,depending upon the reaction temperature and the nature of the reactants.Other things being equal, increasing the molecular weight of the organocomponents of the reactants tends to reduce the reaction rate andincrease the needed reaction time. Generally speaking, the higher thereaction temperature the shorter the reaction period.

The reactions of the present invention can be carried out in the absenceof any solvent, but the use of a solvent results in improved mixing ofthe reactants and in a higher product purity. Consequently, such use ispreferred. Any solvent may be used which is inert with respect to thereactants and the product or products and which is liquid under thereaction conditions.

The solvents employed may include aromatic hydrocarbons such as benzene,toluene and the xylenes; saturated aliphatic hydrocarbons such asn-hexane, isooctane, trimethylhexane, n-dodecane and n-cetane; saturatedcycloaliphatic hydrocarbons such as cyclopentane, cyclohexane, andcycloheptane; saturated aliphatic ethers such as diethyl ether,diisobutyl ether, diisoamyl ether, di-noctyl ether, ethyl heptyl ether,ethyl isoamyl ether and the dimethyl and diethyl ethers of diethyleneglycol; aromatic ethers such as diphenyl ether, anisole and phenetole;hydrocarbon sulfides such as diethyl sulfide, di-npropyl sulfide,di-sec-butyl sulfide and diphenyl sulfide; and tertiary amines such astrimethyl amine, triethyl amine and tri-n-butyl amine. When thereactants are the ethyl derivatives or other low-boiling derivatives ofberyllium and dihorane, toluene is the preferred solvent because itsboiling range is such as to facilitate the separation of the reactionproducts.

Either of the reactants can be added to the other depending on theparticular reactants in use. However, when the ethyl derivatives areused, it is preferred to add the beryllium reactant slowly to the boronreactant to assure an excess of the latter, particularly at the end ofthe reaction. This order of addition is preferred because ofditficulties inherent in the separation of excess organoberylliumreactant from the reaction mixture.

The reaction of this invention may be carried out under any atmosphereinert to both reactants and products but dry nitrogen is preferred.Other suitable protective atmospheres include dry hydrogen, carbonmonoxide, helium, neon, argon, krypton and xenon.

The beryllium hydride obtained by the process of this invention is auseful intermediate in the preparation of beryllium alkyls byolefination as described, for example, in US. 2,826,598, issued Mar. 11,1958, to Ziegler and Gellert. It can be used for the metal plating ofsuitable substrates by thermal decomposition under suitable conditionsin contact with said substrates. It is useful as a source (by thermaldecomposition) of pure metallic beryllium for use both in alloys and asa chemical raw material.

The beryllium bis(dialkyl borohydrides) prepared by the process of thisinvention are highly useful as organo metallic reducing components ofZiegler-type catalysts for making polyethylene, polypropylene andsimilar polymers. Typical examples of such catalytic systems arecombinations of beryllium bis(diethylborohydride) with titaniumtrichloride, titanium tetrachloride and vanadium trichloride,respectively.

These borohydride products are also useful as intermediates in thepreparation, by olefination of the complex, of higher beryllium alkylsfrom those of low molecular weight.

We claim:

1. Process for the preparation of beryllium bis(dihydrocarbylborohydride) of the general formula Be z z) 2,

wherein R represents a radical selected from the group consisting ofalkyl, monocyclic cycloalkyl and monocyclic aryl radicals containingfrom 1 to about 10, 5 to about 10 and 6 to about 10 carbon atoms,respectively, which comprises adding a dihydrocarbyl beryllium compoundof the general formula R Be to a minor excess of a tetraorganodiboraneof the general formula R B H said addition being carried out at atemperature in the range of from about 0 to about C., maintaining thereaction mixture at said temperature for a period ranging from less than0.25 to more than 24 hours, sufiicient to assure the substantialcompletion of the reaction and recovering the berylliumbis(dihydrocarbyl borohydride) from the reaction mixture.

2. Process for the preparation of beryllium bis(diethyl borohydride)which comprises adding diethyl beryllium to a minor excess of tetraethyldiborane, said addition being carried out at a temperature in the rangeof from about 0 to about 110 C., maintaining the reaction mixture atsaid temperature for a period ranging from less than 0.25 to more than24 hours, sufficient to assure the essential completion of the reaction,and recovering beryllium bis(diethyl borohydride) from the reactionmixture.

References Cited Campbell, Jr.: J. Am. Chem. Soc., vol. 79, pp. 4023-4029 (1957).

Websters Seventh New Collegiate Dictionary, 1963, p. 22.

LELAND A. SEBASTIAN, Primary Examiner

1. PROCESS FOR THE PREPARATION OF BERYLLIUM BIS(DIHYDROCARBYLBOROHYDRIDE) OF THE GENERAL FORMULA